The present invention relates to the angular displacement monitoring, more specifically, to an electromagnetic method and apparatus for measuring angular position and a rotation speed of the axial parts of different mechanisms.
The usefulness of the RF or microwave field application for angular displacement and rotation speed monitoring is recognized by the prior art. Such devices can operate with either RF or microwave excitation. When an electromagnetic field is excited near the rotating part of a mechanism, the parameters of the electromagnetic field, such as resonant frequency, phase or amplitude, vary with the change of angular position of the rotating part. The electromagnetic field parameters may be converted into angle, angular speed or rotation frequency. In particular the state of the art is shown in U.S. Pat. No. 3,939,406 xe2x80x9cSensing Rotational Speed by Amplitude Modulating a Continuous Microwave Signal,xe2x80x9d/F. W. Chapman, F. E. Jamerson, and N. L. Muench, 1971, disclosing an electrodynamic sensor including two cavity resonators, one connected to a microwave generator, the other connected to microwave receiver, the two cavity resonators placed near a muff installed on the rotating part, said muff has identical slots in a cylindrical surface along generatrix and positioned periodically in the angular direction. The rotation of the slots influenced by the angular displacement of the muff, leads to a change in the electromagnetic connection between the resonators and, as a result, to the amplitude modulation of the signal passing from the microwave generator to the receiver. The modulation frequency is proportional to rotational speed.
A general discussion, see V. A. Viktorov, B. V. Lunkin and A. S. Sovlukov, xe2x80x9cRadio-Wave measurementsxe2x80x9d [in Russian], Moscow: Energoatomizdat, 1989, pp.148-153, states that a microwave resonator is placed near the rotating part, which surface electrodynamic property (xe2x80x9celectrodynamic profilexe2x80x9d) changes, in the azimuth direction and the resonator""s frequency has a direct correlation to the angular position of the rotating part.
Slowed electromagnetic waves and slow-wave structures are also well known in the field of microwave engineering, see J. R. Pierce, xe2x80x9cTraveling-Wave Tubesxe2x80x9d D. Van Nostrand Company, Inc., Princeton, N.J., 1950. These waves are electromagnetic waves propagating in one direction with a phase velocity vp that is smaller than the light velocity c in a vacuum. The relation c/vp is named slowing or deceleration and is designated as n. In the most practically interesting cases, slowed electromagnetic waves are formed in slow-wave structures by coiling one or two conductors, for example, into a helix, or radial spiral (prior art), which increases the path length traveled by the wave. The curled conductor is named xe2x80x9cimpedance conductor,xe2x80x9d the other is named xe2x80x9cscreen conductor.xe2x80x9d Additional deceleration was also obtained due to positive electric and magnetic coupling in coupled slow-wave structures, which both conductors are coiled and have configuration of mirror images turned by 180xc2x0 relatively to the plane of symmetry, see Yu. N. Pchelnikov, xe2x80x9cComparative Evaluation of the Attenuation in Microwave Elements Based on a Spiral Slow-Wave System,xe2x80x9d Soviet Journal of Communication Technology and Electronics, Vol 32, #11, 1987, pp. 74-78.
The slow-wave structure-based sensitive elements are known in the art, see V. V. Annenkov, Yu. N. Pchelnikov xe2x80x9cSensitive Elements Based on Slow-Wave Structuresxe2x80x9d Measurement Techniques, Vol. 38, #12, 1995, pp. 1369-1375. The slowing of the electromagnetic wave leads to a reduction in the resonant dimensions of the sensitive elements and this enables one, by using the advantages of electrodynamic structures, to operate at relatively low frequencies, which are more convenient for generation and are more convenient for primary conversion of the information signal, but sufficiently large to provide high accuracy and high speed of response. The low electromagnetic losses at relatively low frequencies (a few to tens of megahertz) also helps to increase the accuracy and sensitivity of the measurements. The slowing of the electromagnetic wave leads also to energy concentration in the transverse and longitudinal directions, that results in an increase in sensitivity, proportional to the slowing down factor n, see Yu. N. Pchelnikov, xe2x80x9cNontraditional Application of Surface Electromagnetic Wavesxe2x80x9d Abstract Book, First World Congress on Microwave Processing, 1997, pp. 152-153.
Both the prior art and the present invention measure one or more parameters of electromagnetic field. Some of the prior art methods and present invention use one or two resonators, placed near the rotating part, having an xe2x80x9celectrodynamic profile.xe2x80x9d The resonators are connected to a measuring circuit comprising an RF or microwave signal generator which is used to excite an electromagnetic field. The change in rotating part position causes a shift in the characteristics of the electromagnetic field in the resonators. See V. A. Viktorov, B. V. Lunkin and A. S. Sovlukov, xe2x80x9cRadio-Wave measurementsxe2x80x9d [in Russian], Moscow: Energoatomizdat, 1989, pp.
Devices used in the prior art exhibit several problems overcome by the present invention. Previous methods have low accuracy, sensitivity, and resolution at relatively low frequency, increasing only with frequency increase. However, the increase in frequency is accompanied by an increase in electromagnetic losses, such losses causing a loss of accuracy of the measurement. It is also known that the higher the frequency is, the higher the cost of electronics. The previous methods do not yield the direction of the rotation, and require complex and expensive equipment. Thus, there is a need in the art for an electromagnetic method and apparatus for monitoring rotation that has greater sensitivity, resolution, diversity and lower cost.
The present invention employs a slow-wave structure as a part of a resonator sensitive to position of the rotating surface, parameters of the electromagnetic field in the resonator being informative parameters of position, velocity and the like. The main advantages of such sensitive elements, in comparison to known ones, are: relatively low frequency, concentration of electromagnetic energy in a small volume, the independence of their electrodynamic parameters upon the electronic circuit parameters.
Frequency decrease is achieved due to slowing. Sensitivity increase is achieved due to electromagnetic energy concentration near the rotating surface and due to shifting the electric or magnetic field in the region between the resonator and rotating surface having special electrodynamic profile changing along the azimuth direction. The direction of rotating is obtained due to using non-symmetrical electrodynamic profile, or due to using of two identical resonators placed with angular shift one to another, and comparing electromagnetic parameters of both resonators. The simplicity and inexpensive construction are due to relatively low frequency which allows the printed-circuit processing application. The high accuracy and resolution are due to the resonators"" design: the slow-wave structure-based resonators are made, as a rule, on dielectric base, stable to temperature alteration and its electromagnetic parameters dependence on temperature is very small, contrary to, for example, cavity resonators.
The present invention teaches an electromagnetic method of measuring the position of rotating surface, rotation speed and its direction or other measurements that require high resolution wherein: an excited electromagnetic wave with a preset distribution of the electric and magnetic components of the electromagnetic field makes it possible to increase the sensitivity and accuracy of measurement, using relatively low frequencies. The method is implemented in an apparatus, for example, encoders, wherein: the structural form of the resonators, used as the sensing element and the electrodynamic profile of the rotating part allow increased sensitivity and accuracy. In the invention resonators include at least one section of a slow-wave structure sensitive to the electromagnetic parameters of the electrodynamic profile rotating with a monitored part.
It is known, that the dielectric or conducting materials, placed in the electromagnetic field, alter its parameters, for example, its velocity, that leads to the phase delay or resonant frequency alteration. The influence of dielectric, conducting, and magnetic material differs and depends on electric and magnetic fields distribution in the monitored volume, see V. A. Viktorov, B. V. Lunkin and A. S. Sovlukov, xe2x80x9cRadio-Wave measurementsxe2x80x9d [in Russian], Moscow: Energoatomizdat, 1989, pp. 148-153. Application of slow-wave structures makes it possible to alter electric and magnetic field distribution in the transverse and in the longitudinal directions both, including the electric and magnetic fields splitting. It leads, from one hand, to the sensitivity increasing, and, from the other hand, to electromagnetic field parameters dependence on electromagnetic parameters of conducting or non-conducting objects being in the field of a slow-wave structure-based resonator.